6 Answers
6

It doesn't fit all your criteria, but I use iAnnotatePDF. I can import a script in pdf format and write on it, drop markers and notes, highlight passages. I don't think it's completely ideal but it does work fairly well for me.

Definitely look at GoodReader for iPad. It's a fantastic app for reading most major formats, including doc and pdf. Moreover, it allows you to circle, highlight, annotate and draw on the documents on a separate layer, and in most standard colors. I work a lot in theater and use it all of the time to take sound notes during tech rehearsals.

If you need something that can be edited and changed on the fly, look into Fountain. Not great for all on set, oriented towards writing, but it uses markdown-style annotations to store scripts in raw text for maximum compatibility.